Recent studies have demonstrated the importance of the formation of a hydrated aluminum polymolybdate when a catalyst is prepared by impregnating gamma-alumina with an aqueous solution of ammonium heptamolybdate [Carrier, X.; Lambert, J. F.; Che, M. J. Am. Chem. Sec. 1997, 119, 9, 10137-10146]. We show here how a simple (H-1) Al-27 CP MAS NMR experiment performed in the intermediate regime can easily reveal the formation of a hydrated aluminum polymolybdate on the surface of alumina. Taking, simultaneously, advantage of the differences in dipolar polarization transfer and those in quadrupolar effects on spin-locking efficiency, it is possible, after setting the experimental parameters on reference compounds, to partially suppress the signal resulting from the alumina support at 8.5 ppm while enhancing the 14 ppm resonance of the aluminum polymolybdate. In this way, the occurrence of a hydrated polymolybdate is evidenced, not only on samples impregnated with (NH4)(6)Mo7O24 but also with Na2MoO4. Furthermore, a dialysis experiment proved that a dissolution/reprecipitation mechanism is at least in part responsible for the formation of the AI-O-Mo bond.